He said: "I do feel like there is something that is exotic to an American audience. It's funny, the royal family here has a mixed impression with the general public.

"You go to America and anything royal is instantly embraced, we can't get enough of it.

"The world of class... we don't necessarily have it in such an overt way in the US, so it doesn't ring true.

"In the US we don't really talk so much about upstairs or downstairs. It's just Downton and they're all characters to us."

Executive producer Gareth Neame recalled being told that nobody in the US would ever be interested in Downton.

The drama has become a worldwide commercial and critical success.

It is the highest rating UK television drama of the past decade, with an average of 11 million viewers over the course of the last five series. The show was presented with a Bafta special award, in recognition of its contribution to television in the UK and around the world.